Hi Wink,
The guards you've used look sufficient (though it's mildly concerning that any poor user who received your libsel4's
assert.h before libc's has their asserts unconditionally become no-ops). We also previously explored the option of using
different typedef names, but felt it led to unnecessary confusion when reading the stubs. I'm not debating whether these
things can be checked for at compile time, but IMHO the necessary checks in a large build system are more complex than
one might initially imagine.
I don't have any objection to minimal systems and probably no one who works on microkernels does. Personally I think
implementing a C application without including libc is signing yourself up to re-implement libc, but if you're OK with
that than fair enough. I'm not opposed to the idea behind this proposal, of removing the libsel4->libc dependency, but
since I am unlikely to be the one maintaining it, I'll leave it to others to make a call on whether to go in this direction.
Cheers,
Matt
On 23/06/15 21:03, Wink Saville wrote:
Matt,
I've guarded the definitions with conditionals to try to avoid that, but maybe
a better option might be to use different
names completely. Also, we could test for compatibility at compile time and
generate errors.
My rational for wanting this is that libc doesn't seem to be providing that
much value as very few of its vsyscalls are
implemented anyway. Thus its utility is actually small, IMHO. Also, I happen to
be interested in minimal systems so
unused and extraneous code is an anathema. Here, in libsel4, by adding these few LOC's we
are removing "thousands" of
LOC brought in by the need of a libc.
Anyway, I'd certainly like to keep the discussion going to revisit the the
earlier decision, I just feel strongly the
less code the better.
On Tue, Jun 23, 2015, 12:02 AM Matthew Fernandez <[email protected]
<mailto:[email protected]>> wrote:
Hi Wink,
As you've observed in that commit, removing the libc dependency leads you
to re-implement pieces of it inline. We used
to do something similar to this, but replaced this with an explicit
dependency on libc to avoid complications with
multiple definitions of typedefs and such. In the case of programmer error,
these typedefs may not match and if the
conflicting typedefs are never seen within the same translation unit your
compiler will not notice either. The end
result was subtle bugs arising from ABI incompatibility.
When we made the change, out rationale was that anyone using the syscall
stubs would have libc available anyway. This
certainly introduces a circular dependency, but it's not easy to remove
without repeating parts of one library in the
other or playing tricks with externs and weak symbols. In my experience,
all of this is more fragile and less preferable
than living with the circular dependency. However, my opinion may not be
universally shared as we haven't had a
discussion about this for some time.
Cheers,
Matt
On 23/06/15 11:16, Wink Saville wrote:
> I noticed that seL4/libsel4 was dependent upon libc and so I created a
patch
>
(https://github.com/winksaville/seL4/commit/fc91a1f68c054fdb41aaa42a7b56a80f481b68b2)
which removes the
dependency. If
> there is interest I can submit a pull request, and of course will make
any changes deemed necessary to make it
suitable
> for acceptance.
>
> Please advise,
>
> Wink
>
>
> _______________________________________________
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>
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